Shunt for low-voltage circuit testers



March 30, 1954 oz -r 2,673,957

SHUNT FOR LOW-VOLTAGE CIRCUIT TESTERS Filed July 6 1951 2 Sheets-Sheet l .l' l 4 P51067770? jerzjzmz'zz $021972? March 30, 1954 B, ROZETT 2,673,957

SHUNTVFOR LOW-VOLTAGE CIRCUIT TESTERS Filed July 6, 1951 I 2 Sheets-Sheet 2 Patented Mar. 30, 1954 v 1 7 72,673,957, 7 c a I SHUNT'FOR: now-vg men CIRCUIT Ben am n lozcttflhi ago, I l-l ss sts): mi s n e n fl co n a dha \w nq a ion at.

Illinois- Anaemia ,'-i r fir @1;N0-' 235,466.

a-"claim 01. 324 12 This invention relates topircuit testingappa ratuswand morev particularly to, apparatus forf making low voltagecircuit tests. 1

This application is, agcontinuationsins-partI of, my application. Serial Hal-44,906 f led: August 18, 1948, now Patent2597 183;which-issued lwayjfi,- 19,52

Qne feature v, of this inventionv is that "it pro vides circuit testing apparatus; whereby all-,neces-.- sarylow voltagecircuit ,tes ts may be performed on a vehicle, as for example, a tank by a unitary portable device; another feature, of this; invention-Visthat it provides, circuit testing apparatus comprising an. ammeter having a; plurality, of ranges, and including-selectively useabl fixed resistances for per-forming certain? tests, a voltmeters having; a plurality 01E ranges, and app aratus: for testing; a battery or, rgeneratonand all; otherdevices included inthe; primary, circuit under load or otherwise ,a still; anotherr-feature of c this; invention is; that while; a plurality I of meterranges are provided each range-;is connectable u means of a differ nt term nal-h thereby 6 1K1 7 hating all switches with their attendant disad vantages an additional- :feature of this invention. is that 1 it provides; an ammeter-havinga con: tinuous; one pieceorsinglestrip;ammeter shunt. which may .be easilycalibratediin spiteof slight. variations in the thicknessofithe metal; a fur: ther feature is thattheiammeter ind napos s- 01-1. connector posts: are directly connected.- to, the one piece shunt; another feature; 0f;-:t.he= invent-i. tion -is that the ammeter shunt; has aplurality of terminalsin series with. a. commonterminal;

still aifurtheifeature of; the invention is that it provides three external terminals adapted.v to:- provide connectionsfor external shunts; in which event the. internal shunts mentioned above are. IlOlOngel used as such. in parallel with the meter; but are all connected in series therewith; and still sin-additional feature of ther inventionis that it provides a meter having a. plurality of" ranges and a scale comprisinga-combination (of different indiciatd provide-indications over a plurality of ranges.

Other features and advantages of theinventionwill be apparent from -the following Specifi cation and fromthe drawingsinlwhich: V

Fig. leis a frontelevational viewof. mysimproved circuit testing apparatus;

Fig; 2 is a top plan viewithereot;

Fig; MS a sectional'plan view, partially broken-i showing the meters and the, extentito which the terminals: project 7; beyond 1 the, meters faces v Fig. 4 is a sectional view of the apparatus illuse inae. m enshunt a th ng or the meters;-

E ifiais atschematiQ-d aeram-,o he r uit-pi: the appa srand;

s 6 is asec ion i. ie o on oi, he esisto ccilsme in ek ona Jack-1 n; mak sl iv a e es s, fi he. lect ica ys m gi ehi le i. s; or; xam ev h elect ivl-sys em. f a a on dminis ive.-vehic es tisnece ary o. ma e urr nt; or m rage test$;. d o ta e-t sts v n a.: wlura y ofz. an es., In th past-hmsingle; ni ary:por blei e inadevice as e n; devised; for ma ineial of; he: necessar ts. nd; mos mfr the de ces: which have een; s n p f m nez heltes ain-saddition qheine; ncap le of pe -forming: all; he uir d tests have. ad-.disadv n asesin the they w re easily broken, nerally:= inc udedeswitchine arran r ments between; the ranges and; included; numeru ifie nt 56 1983150 coverthe various,.,,-meter ranges, Where the apparatus is: subjected tocex reme =.-.c1imaticconditions;as for'example thehot, humid; climate foundsimAf-rica, or in; the Pacific- Islands, the switch: contacts in such meters often develop highi-resistance ranch-quickly, destroy the. accuracy -of:the meters. V

I have devised and; am herewith disclosin and claiming, improved circuit testing apparatus pare. ticulanly designed to perform all thellowvoltage tests which may be required; in a. vehicle, as for example. in. a tank. or: administrative vehicle. My apparatuscomprisesi a compact unitaryport able structure which is protectedifrom damage in the event it. is inadvertently knocked over; which eliminates. the switching;- arrangements formerly found; and' which: is very readily I used. by a relatively unskilled operator and. which includes a novel: scale arrangement providing readily-readable indications over-a pluralityof meter ranges with a-m-inimum of scal'es; The apparatus illustrated is adapted toperform the following tests inthe low voltage-circuits of a tanker other vehicle: tests for voltage drops over all oral y of he ri us r on of: he QW volta e circuit; tests of the, battery and the individual cell. voltc ages; both withsand.withoutload; tests oflthe starting motor, as. for examplethe. current draw under normal conditions and under: loci: torquev wher theltank is in ear, and rake d:

ener ie: outwit a aria s EQQQ sis hi: the; ontrol equipment; and

all other electrical functions of the low voltage circuits.

Referring now more particularly to the drawings the apparatus comprises a casing having a main body portion ID, a cover I I connected to the casing It by means of a hinge I2. The cover Il may be maintained in closed position by means of a pair of clasps l3. A handle 14 secured to the body portion I0 is used to carry the apparatus. The main body portion I0 includes a back I and a front or face portion IS. The interior of the cover II is utilized to carry testing accessories, as for example, leads, shunts, etc. The front portion It is secured to the body portion Ill by means of screws H which connect the front portion It to angle support members (not shown) connected to the main body portion ID.

The front portion I6 carries a plurality of terminals I9c-I9r which project from the face of the casing a substantial distance as shown in Fig. 3 for a purpose to be hereafter described. The casing houses an ammeter 2I which has an indicating portion 2Ia in the face It of the easing, and a volt meter 22 which has an indicating portion 220. in the face of the casing.

The ammeter circuit may best be seen in Figs. 4 and 5. One side of the ammeter is connected to a common terminal I90, through a circuit of negligible resistance, this circuit including a lead 26 connected between the positive side of the meter (in the views shown) and the terminal I9e and a lead 21 connected to the common terminal I9a. This common terminal is connected to the other or negative side of the ammeter through a plurality of ammeter shunts incorporated in a single strip of material 23.

The single strip ammeter shunt 28 is composed of a conductor having a sufficiently high resistance for its effective operation as a shunt.

A plurality of slots ZBa-e control the resistance in any particular portion of the strip 28 and it is to be noted that each portion set off by the slots contains a terminal. Since it is desired that the resistance between the terminals Mia and I9!) be the same as the resistance between the terminals I9b and I90, the slots 28a and 28?) are of equal length. However, it is desired that the resistance between the terminals I90 and 19d be higher. Consequently, there are three slots Etc-48c between these two terminals, the slots :11

28c and 28a being from one side of the strip and the slot 28d bein from the other side of the strip.

It may be seen that the path for the current to travel between terminals I90 and H11 must pass in the narrow area between slots 28c and 28d and slots 28d and 28a. This longer path through a high resistance of narrowed cross sectional area will naturally result in a considerable increase in the resistance between the terminals I90 and I901 as compared with the resistance between the terminals I9a and I9b or I9b and I90. In this way the spacing of the terminals on the shunt strip may all be equal and yet the resistances between terminals be quite different.

.In order to provide an accurate ammeter it is necessary that the resistances of the various portions of the shunt strip be carefully controlled. An example of how this may be done will be described with reference to the slot 28d. When the shunt strip is initially prepared, as by being stamped out, the slot 28c is not out to its full required length but rather to a length where the resistance between the terminals I90 and H11 is lower than that desired. The terminals I90 and HM are then connected with an instrument which is very accurate in determining the resistance between the two terminals. The slot 286 is then very carefully increased in depth by a hand-controlled cutting means until the resistance between the terminals I and I9e has reached the desired level. It is possible in this way to calibrate a shunt strip with great accuracy. Applying an insulating protective coating to the shunt strip will then help to keep its resistance properties constant.

The terminal I90, which in the apparatus illustrated may be connected to provide a 50 ampere range on the meter, is connected to the negative side of the meter through only a portion of the shunt strip. Obviously, if is is desired to use the meter on a 50 ampere scale, the terminals I91; and I90 are connected in series in the circuit to be measured and with this arrangement, the portion of the shunt strip between the terminals I9a and I90 will be shunted across the series combination of the meter and the portion of the shunt strip between terimnals I90 and led. The terminal I9b is designed to provide a ampere range on the meter while the terminal I9d will provide a 10 ampere range.

Obviously, as many ranges as desired may be provided without switching, the construction being such that the various ranges are made by using all or certain portions as desired of the shunt strip across the series combination of the meter and the remaining portion of the shunt strip, if any.

In addition, to the internal shunt consisting of the shunt strip 28 an external shunt may be connected to the meter circuit by means of plugs. The terminal I9e is like that illustrated in Fig. 6 and includes a 3-ohm resistance 3|. The terminal I9e is a common terminal when th external shunt is used. When the external shunt is used the millivolt drop across the shunt is impressed upon a series circuit, one portion of the series circuit being the three-ohm resistance of terminal I9e and the other portion being the parallel combination of the internal shunt strip 28 and the meter.

The external shunt gives a dual range. In order to do this the negative lead from the ammeter 2| is shifted so as to include a dropping resistance which allows only the desired portion of the voltage drop across the shunt to be impressed across the meter. Thus, a higher current must flow through the shunt to give the same meter deflection.

In order to use the meter for the 500 ampere range an external shunt will be connected from the terminal I9e to the terminal IBg. If a range of an order of 1000 amperes is to be used an external shunt will be connected from the terminal I9e to the terminal I91. The terminal ill incorporates a resistance element 32 which also is of the type shown in Fig. 6. This dropping resistance is preferably of the order of 2.13 ohms in the circuit shown. Where the 1000 ampere range is used the current to the meter flows through both the 2.13 ohm and the 3 ohm resistances.

The provision of an ammeter having a plurality of ranges together with the combination of a selectively operable variable resistance for performing certain tests is novel and results in a device of far greater utility than has heretofore been found in the art since all of the necessary: current tests may be performed by a single device. The further provision of a separate terminal for each range simplifies the use of the apparatus and-aids in preventing the apparatus from being used on the wrong range since it is necessary for the operator consciously to connect the apparatus to the circuit he desires to test, and consequently it is highly unlikely that the ampere terminal l9d would be connected by the operator into a. high current circuit. Furthermore, the provision of the series-connected shunts entirely eliminates the. necessity of switching between shunts, and if the apparatus is utilized in a damp or humid climate there are no concealed switches to corrode, become covered with fungus, or otherwise deteriorate, and there is no possibility that a high resistance will develop across the meter, thus destroying its utility as an ammeter. The necessity of connecting an external shunt for excessive high amperage ranges 'will act as a warning to the operator and remind him that high currents are present, and again it is not necessary to switch between shunts since the three series-connected portions of the shunt strip 28 merely become connectors in parallel withthe meter when a highrange external shunt is connected across the terminals lee and l9g.

Another resistor which may have a value of 1.5 ohms is mounted in the casing, the opposite ends of this resistor being connected to the terminals 19h and I97 while the center tap of the resistor is connected to. the terminal I92. These terminals may be used in making certain tests upon the voltage regulator, the terminals lSh and I92 being connected in the circuit for 6 volt tests and the terminals |9h and 197" being connected in the circuit for 12 volt tests.

The voltmeter 22 is also connected to provide a plurality of ranges. The common (here shown as the positive) side of themeter is connected to the terminal I9k, and the negative side of the meter is connected to the terminals l9m--l9r in paralleL- As illustrated, a resistor 4i, which'may have a value of 50,000 ohms, is connected in series between the terminal Him and the negative side of the meter to provide a volt range; a resistor 42, which may have a value of 20,000 ohms,

is connected in series between the terminal'iiin and the negative side of the meter to provide a range of 20 volts; a resistor, which may have a value of 10,000 ohms, is connected between the terminal I91) and the negative'side of the meter to provide a 10 volt range; and which may have a value of 1,000 ohms, is connected between the terminal I92" and negative side of the meter to provide a one volt range.

Again as in the case of the ammeter there are no switches to be operated in the volt meter circuits and there can be no abnormal high resistance connections which develop because of climatic or other conditions in use, and as the case in the ammeter' circuits it is necessary for the operator consciously to connect a lead to one'fof the terminals in order to operate the meter, thereby minimizing the possibility that the operator will attempt to use the meter across a high voltage circuit when it is arranged to operate 'on one of it lower ranges. The resistances 3|, 32, 4|, 42, 43 and 44 are of the type illustrated in Fig. 6. In this figure a jack protruding from the face l6 of the mounting panel has a receptacle 6! into which'a plug may be inserted. A mounting rod 62 is threadably attached to the jack 6!] on the part which extends through to the back side of the panelflfi. A nut 63 threaded on the mounting rod 62 maintains the assembly in mounted position upon'the a resistor 44,

iii)

colors.

I panel I 6. A resistance coil 64 is wound around the mounting rod 62, thelower end of the coil in the view shown being attached to a solder lug B1. The upper end of the coil 64 is connected through an insulated solder lug 68 to a conductor 65 leading from the negative terminal of the volt meter 22. With this construction, when a plug is inserted in the receptacle 6| a conducting path is set up which passes from the jack 60 through the mounting rod 62 and the resistance coil 54 to the conductor 65. Referring to Fig. 5, it may be seen that the resistance 4| may be in-- cluded in the circuit if plugs are connected to the terminals Him and [97a If it is desired to include the resistance 42 in a circuit, plugs will be connected to the terminals I911 and I970. In a similar manner resistances'43 and 44 may be connected in the circuit.

In addition to the electrical advantages found in my circuit testing apparatus, there are certain mechanical advantages provided. Referring particularly to Figs. 1 and 3 it will be seen that the terminals 59 project a substantial distance from the face of the casing and the arrangement of the terminals on the face is such that the terminals will support the casing in the event the device is knocked over on its face and the indieating portions of the meters (which normally are glass enclosed) will be protected against damage. By this arrangement the same terminals which provide an electrical function are arranged to provide a mechanical advantage not found in other devices.

In addition I have provided an arrangement wherein, despite the large number of meter ranges, a minimum of scales are utilized and each scale comprises a combination of different indicia to provide readily readable indications over a plurality of ranges. Referring rst to the indicating portion 21a of the ammeter 2!, the meter pointer or needle 50 may be adjusted by means of an adlusting screw iii to give a zero reading when the meter is disconnected as shown. Preferably the zero point on the ammeter scale is not at the extreme left of the scale since certain types of apparatus to be tested, as for example reverse current relays, utilize a negative polarity current. Despite the fact that the ammeter illustrated has 5 ranges of maximum deflection, as 10, 50, 106, 500 and 1,000 there are only two scales and each scale provides indications over a plurality of ranges. The top scale may be utilized to read-the current for the ranges of 10, 100 and 1,000 amperes and the bottom scale may be utilized for the ranges of 50 and 500 amperes. I achieve this desirable result by forming the numbers of each scale of a combination of different For example, the second number of each scale marking in the top scale may be formed of a different color than are the first and third numbers, the farthest number to the left in Fig. 1 (the number 300) appearing as a black three, a red zero, and a black zero. Thus when utilizing the 10 ampere range only the first number is used and if the pointer 50 swings to this far left position the operator will snow that a current of 3 amperes is flowing in the circuit. If the range is 100 amperes the black three and red zero will be utilized and the operator will know that 30 amperes are flowing in the circuit while if the thousand ampere range is utilized the operator reads all three numbers and it will be apparent that 300 amperes are ilowing in the circuit. Similarly, on the bottom scale the different colored indicia provide a ready differentiation between the 50 ampere range and 500 ampere range. For example, referring to Fig. 1, the highest number (500) on this scale comprises a black five, a black zero, and a red zero. For the 59 ampere range only the black numbers are used and for the 500 ampere range all the numbers are used. In both the upper and lower scales the reference number at the right end or high end of the scale will show the operator the maximum deflection of the range he is working on, thereby minimizing any chance for error.

Similarly, in the voltmeter 22 only three scales are necessary despite the fact that the meter covers four ranges. In this meter, as shown in Fig. 1, a pointer 52 normally zeros at the left end of the scale, an adjusting screw 53 being provided to set the zero point. As shown in Fig. l. the scale at the top is used for maximum deflection ranges of one volt and 10 volts despite the fact that there is only one set of numbers on this scale. I prefer that the numbers be black and that at each unit mark there is a decimal point of a different color, as for example red. Thus when using the one volt scale the operator will read the numbers including the decimal point as indicated by the highest number on the scale, and when using the 10 volt scale the operator will read the black numbers while ignoring the red decimal points, the different colors serving to facilitate the reading of the scale. There are two lower sets of numbers in vertical alignment to provide maximum dc fiection ranges of volts and 50 volts. I prefer that these sets of numbers be of difierent colors, as for example the 20 volt scale utilizing black numbers and the 50 volt scale utilizing red numbers.

While I have shown and described certain embodiments of my invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as disclosed in the appended claims.

I claim:

1. In circuit testing apparatus having an ammeter, shunt means of the character described,

comprising: an elongated strip of resistance material providing a meter shunt operably connected to said ammeter; and at least three terminals directly mounted in spaced relation on said strip of resistance material, providing a plurality of ranges for said ammeter.

2. In circuit testin apparatus having an ammeter, shunt means of the character described, comprising: an elongated strip of resistance material operably connected to said ammeter, providing a meter shunt; a first terminal directly mounted on said strip of resistance material at one end thereof; a second terminal directly mounted on said resistance strip at the other end thereof; and at least one terminal directly mounted on said resistance strip at a point intermediate said first and second terminals, there being at least one transverse calibration slot cut in said resistance strip between each pair of terminals.

3. In circuit testing apparatus having an ammeter, shunt means of the character described, comprising: an elongated rectangular strip of resistance material operably connected to said ammeter providing a shunt therefor; a first terminal directly mounted on said resistance strip at one end thereof; a second terminal directly mounted on said resistance strip at the other end thereof; a third terminal directly mounted on said resistance strip at a point intermediate said first and second terminals; and a fourth terminal directly mounted on said resistance strip at a point intermediate said second and third terminals, there being a plurality of transverse calibration slots cut in said resistance strip and extending inwardly from a longitudinal side thereof, at least one of said slots being between each adjacent pair of terminals, said first and second terminals providing a low range ammeter, said first and fourth terminals providin a medium range ammeter and said first and third terminals providing a high range ammeter.

BENJAMIN ROZETT.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 846,969 Wohl Mar. 12, 1907 892,554 Roller July 7, 1908 1,705,301 Miller Mar. 12, 1929 1,901,343 Eastham Mar. 14, 1933 1,951,799 Lederer Mar. 20, 1934 2,183,617 Kurz r Dec. 19, 1939 2,384,350 Skulley Sept. 4, 1945 2,507,803 Miller r May 16, 1950 FOREIGN PATENTS Number Country Date 16,159 Great Britain July 22, 1903 of 1903 3,809 France Feb. 25, 1905 (Addition to No. 319,883) 367,085 Great Britain Feb. 18, 1932 770,413 France Sept. 13, 1934 770,781 France Sept. 20, 1934 641,381 Germany Jan. 29, 1937 OTHER REFERENCES Publication, Radio Master, published by United Catalog Publishers, Inc., New York city 13, N. Y., Copyright 1944, pages F 27, N-3. (Copy in Div. 69.)

Publication, "General Electric Review, published by General Electric Co., June 1946, page 58.

(Copy in Div. 69.) 

